a high clocked e8400 is better in game then a q6600. and the xigmatek is extremely good for the price. as in top 5 coolers.
for most games they are the same or the difference is minuscule, except for games like supreme commander where quads are better. Dual core is old, quad core is alot more future proof and offers same performance right now in most games. q6600 is much better option stick with it.